Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
phthĭsis, is, f., = φθίσις, consumption, phthisis: vera phthisis est, Cels. 3, 22; Sen. Ep. 91, 5; 75, 10; Plin. 26, 7, 21, § 38; 31, 6, 33, § 62; Col. 6, 14; Juv. 13, 95; Gell. 4, 2, 4.